Several aspects of the development of oral-facial organs and tissues are under active investigation: 1. Various tissue recombinations, and treatments with exogenous materials are being employed in an effort to understand and analyze the emerging morphology of the embryonic tooth rudiment. Concomitant study of the cytological characteristics of the ameloblasts and odontoblasts as they differentiate under normal and abnormal environmental conditions compliment the in vitro studies of the intact organs. 2. Studies of the development of the secondary palate in vertebrate embryos also employ homologous and heterologous tissue recombinations in an effort to reveal the tissue cooperations which occur as normal processes during ontogeny. 3. Investigations into the origins and differentiation of the tissues of the cranial regions of the early mammalian embryo are currently focused upon the ultrastructural characteristics of the individual cells--particularly the cells of the trigeminal ganglion. BIBLIOGRAPHIC REFERENCES: Smiley, G.R. and W.E. Koch. 1975. A comparison of secondary palate development with different in vitro techniques. Anat. Rec. 181: 711-724. Tyler, M.S. and W.E. Koch. 1975. In vitro development of palatal tissues from embryonic mice. I. Differentiation of the secondary palate from 12 day mouse embryos. Anat. Rec. 182: 297-304.